A mass includes particles that exhibit an in vivo lifetime and that include a bioresorbable material and bubble cavities disposed in the particles, wherein the bubble cavities have length, width, and height dimensions at least one of which is less than or equal to about 2000 microns. The mass exhibits enhanced detectability by ultrasound energy during the lifetime the lifetime begins upon exposure to in vivo fluids and ends between about 2 and about 20 weeks afterward and a zero or non-zero fluid-to-solid ratio.
